The present invention relates in general to methods for fabricating semiconductor and other microelectronic devices. More specifically, the invention relates to microlithographic methods as used in manufacturing microelectronic devices. The microlithographic methods are performed using a charged particle beam (e.g., electron beam) and a divided mask or reticle (termed xe2x80x9creticlexe2x80x9d herein) defining a pattern, wherein the reticle is divided into multiple subregions defining respective portions of the pattern. Dividing the pattern involves splitting certain pattern elements into respective pattern-element portions located in different subregions, wherein exposure of the pattern involves re-joining (xe2x80x9cstitchingxe2x80x9d) the pattern-element portions together as the images of the subregions are projected onto the surface of a wafer, thereby forming the complete pattern on the surface of the wafer.
Usually, whenever a pattern for a microelectronic device is formed in a resist on the surface of a wafer using an electron-beam exposure (microlithography) apparatus, a stencil reticle is employed. A stencil reticle also is termed a xe2x80x9cperforated reticlexe2x80x9d in which through-holes in a membrane define respective pattern elements. The through-holes transmit the electron beam in accordance with the respective shapes of the pattern elements. However, there are limits to the area that can be transferred at one time using a single reticle. Furthermore, a xe2x80x9cdonutxe2x80x9d pattern element cannot be defined in a single subregion of a stencil reticle because the middle portion of the element is unsupported and falls out. Moreover, if a pattern element is very large, the stencil reticle portion defining it tends to deform.
Accordingly, for certain pattern elements to be defined using a stencil reticle, the pattern element as designed usually is split into portions defined in separate respective subregions of a reticle. Exposure of the separate subregions is performed successively by irradiation using an electron beam or other charged particle beam. Successive exposure requires that the reticle subregions be successively positioned for exposure using an electron-optical system. Thus, the pattern elements defined by the reticle subregions are transferred to a resist layer on the surface of a wafer. The subregions defining the pattern-element portions are transferred one at a time by deflecting the electron beam, or by moving the respective positions of the reticle and wafer. As a result, the plurality of split pattern elements are exposed adjacent to each other to recreate the entire pattern, as designed, on the wafer.
FIGS. 16(a)-16(c) and 17(a)-17(c) show examples of split pattern elements. In cases where the pattern element is designed as a hollow xe2x80x9cdonutxe2x80x9d-shaped element as shown in FIG. 16(a), the element as defined on the reticle is split into the two portions shown in FIGS. 16(b) and 16(c) to prevent the center portion from dropping out. In cases where the pattern element as designed is a long linear element as shown in FIG. 17(a), the element as defined on the reticle is split into the respective portions shown in FIGS. 17(b) and 17(c) to prevent deformation of the reticle. The element portions are exposed adjacent each other on the wafer so that the entire pattern element as designed is transferred onto the wafer.
Whenever pattern elements are transferred in portions, as described above, there are limits to the accuracy with which the pattern-element portions split on the reticle can be aligned on the surface of the wafer. Accordingly, whenever a plurality of split pattern elements are exposed while being positioned adjacent to each other or overlapped with one another, a considerable amount of positional deviation may occur. Pattern-element deformation caused by such positional deviation is a cause of faulty connections between pattern elements and of wiring interruptions, etc., and is a major problem in the manufacture of modern microelectronic devices having ultra-fine patterns.
A conventional method for preventing breaks in transferred pattern elements involves overlapping the interconnecting portions of the pattern elements, as shown in the shaded areas in FIG. 17. However, whenever portions of pattern elements are overlapped in this manner, the line width of the portions subjected to overlapping exposure is increased, as shown in FIG. 17. Furthermore, as a result of variation in the amount of overlapping caused by positional deviation errors of pattern elements as exposed onto the wafer, the degree of thickening of the line width also varies.
Japan Patent No. 2,706,099 discloses a procedure directed to this problem. Specifically, whenever adjacent portions of a pattern element are connected to each other, a first protruding part (that is smaller than the normal line width of the element in relative terms) is formed at the mating end of one of the portions. A second protruding part having a shape exhibiting linear symmetry with the first protruding part is formed at the mating end of the other portion. However, no approach for optimizing the shapes of the mating ends has been established in cases where the respective shapes of mating ends of pattern elements are finely worked.
In particular, in cases where protruding parts are formed in the mating ends of respective pattern-element portions, and the pattern-element portions are joined together by overlapping the protruding parts of these ends, the widening of the line width in regions of the mating ends subjected to multiple exposure depends greatly on the degree of blur of the exposing beam. Since beam blur of an electron-beam lithographic exposure apparatus varies with changes in the space-charge effect and other phenomena, the dimensions of the protruding parts formed in the mating ends of pattern elements cannot be made the same at all locations on the reticle. Also, the line width varies in areas occupied by mating ends whenever the degree of beam blur varies due to instability of the electron-optical system.
In light of the above, an object of the invention is to provide microelectronic-device fabrication methods exhibiting reduced variation, in the line width of interconnected mated ends of elements of a pattern, that otherwise occurs whenever the pattern is defined by multiple split-pattern portions on respective portions of a reticle, and a charged-particle-beam lithographic exposure apparatus is used to transfer the split pattern elements onto a resist applied as a coating to a wafer, thereby more reliably connecting the multiple split pattern elements together as imaged on the wafer.
Certain methods according to the invention are directed to respective lithographic processes set forth in the context of a method for manufacturing a microelectronic device. The lithographic processes achieve transfer of a pattern to a resist layer on a wafer. The pattern includes pattern elements split among respective reticle subregions that are exposed onto the resist using a charged-particle-beam lithographic-exposure apparatus that places and stitches together images of the reticle subregions on the wafer to form the pattern on the wafer.
According to a first embodiment, in a first reticle subregion, a first pattern-element portion is defined having a line width and a respective mating end including a protrusion that exhibits increased narrowing of line width toward a distal tip of the protrusion. The protrusion has a length that is 1 to 5 times the line width of the first pattern-element portion. In a second reticle subregion, a second pattern-element portion is defined having a line width and a respective mating end including a recess having a profile that is complementary to the protrusion. The recess has a length that is 1 to 5 times the line width of the second pattern-element portion. Consequently, when the first and second pattern-element portions are exposed onto the resist, the portions collectively form a contiguous pattern element. Using a charged-particle-beam lithographic-exposure apparatus, the first and second reticle subregions are transferred onto the resist in a manner such that the respective mating ends of the first and second pattern-element portions are stitched together in the pattern on the wafer.
The first and second reticle subregions can be on the same or on separate reticles. Also, the protrusion can be shaped such that it progressively narrows toward the distal tip of the protrusion or narrows in a staircase manner toward the distal tip of the protrusion.
According to a second embodiment, in a first reticle subregion, a first pattern-element portion is defined having a line width and a first mating end shaped as a recess flanked by respective protrusions. The protrusions each have a respective rounded tip and a respective width that narrows toward the respective rounded tip. In a second reticle subregion, a second pattern-element portion is defined having a line width and a second mating end that is substantially complementary to the first mating end. The second mating end includes a step region disposed so as to be located, whenever respective images of the first and second pattern-element portions are stitched together, adjacent the respective rounded tips of the protrusions of the first mating end. The second mating end also includes a protrusion extending from the step region and disposed so as to be located, whenever respective images of the first and second pattern-element portions are stitched together, in the recess of the first mating end. Using the charged-particle-beam lithographic-exposure apparatus, the first and second reticle subregions are transferred onto the resist in a manner such that the first and second mating ends are stitched together in the pattern on the wafer. The recess in the first mating end can be defined with a length that is 1 to 5 times the line width of the first pattern-element portion. Similarly, the protrusion of the second mating end can be defined with a length of 1 to 5 times the line width of the second pattern-element portion.
According to a third embodiment, in a first reticle subregion, a first pattern-element portion is defined having a line width and a respective mating end defining a respective protrusion extending at an oblique angle relative to a longitudinal direction of the first pattern-element portion. The protrusion narrows toward a distal tip of the protrusion. In a second reticle subregion, a second pattern-element portion is defined having a line width and a respective mating end defining a respective protrusion extending at an oblique angle relative to a longitudinal direction of the second pattern-element portion. The protrusion has a profile that is complementary to the protrusion of the mating end of the first pattern-element portion. Using the charged-particle-beam lithographic-exposure apparatus, the first and second reticle subregions are transferred onto the resist in a manner such that the respective mating ends of the first and second pattern-element portions are stitched together in the pattern on the wafer. The protrusion of the mating end of the first pattern-element portion can be defined such that the distal tip of the protrusion is rounded. In such an instance, the protrusion of the first pattern-element portion desirably includes a proximal step region situated so as to be adjacent the rounded distal tip of the protrusion of the mating end of the second pattern-element portion whenever the first and second pattern-element portions are stitched together on the wafer. Similarly, the protrusion of the mating end of the second pattern-element portion can be defined such that the distal tip of the protrusion is rounded. In such an instance, the protrusion of the second pattern-element portion desirably includes a proximal step region situated so as to be adjacent the rounded distal tip of the protrusion of the mating end of the first pattern-element portion whenever the first and second pattern-element portions are stitched together on the wafer. The protrusion of the first pattern-element portion desirably is defined with a length of 1 to 5 times the line width of the first pattern-element portion. Similarly, the protrusion of the second pattern-element portion desirably is defined with a length of 1 to 5 times the line width of the second pattern-element portion.
According to a fourth embodiment, in a first reticle subregion, a first pattern-element portion is defined having a line width and a respective mating end including a respective protrusion having an edge extending obliquely to a length dimension of the first pattern-element portion. The protrusion includes a respective recess. In a second reticle subregion, a second pattern-element portion is defined having a line width and a respective mating end that is complementary to the mating end of the first pattern-element portion. Using the charged-particle-beam lithographic-exposure apparatus, the first and second reticle subregions are transferred onto the resist in a manner such that the respective mating ends of the first and second pattern-element portions are stitched together in the pattern on the wafer.
The recess defined in the protrusion of the mating end of the first pattern-element portion can be configured to divide the respective protrusion into first and second protrusion portions that flank the recess, wherein each protrusion portion has a respective rounded distal end. The mating end of the second pattern-element portion can be defined to include a respective protrusion having an edge extending obliquely to a length dimension of the second pattern-element portion. The protrusion desirably includes a recess that divides the respective protrusion into first and second protrusion portions that flank the recess, wherein each protrusion portion has a respective rounded distal end. In the mating end of the first pattern-element portion, the obliquely extending edge desirably includes a respective step region situated so as to be located adjacent a rounded tip of a protrusion portion of the mating end of the second pattern-element portion when the first and second pattern-element portions are stitched together on the wafer. Similarly, in the mating end of the second pattern-element portion, the obliquely extending edge desirably includes a respective step region situated so as to be located adjacent a rounded tip of a protrusion portion of the mating end of the first pattern-element portion when the first and second pattern-element portions are stitched together on the wafer. The recess defined in the protrusion of the mating end of the first pattern-element portion desirably is defined to have a length of 1 to 5 times the line width of the first pattern-element portion.
In the methods described above, portions of pattern elements (i.e., regions of pattern elements where respective pattern-element portions are joined together as projected on the wafer) can be subjected to double exposure due to positional errors. However, undesirable consequences of such double exposures, such as line-width thickening or line-width narrowing, or breaks in pattern elements, are reduced by configuring the mating ends of pattern-element portions (according to certain aspects of the invention) so as to fit together in a complementary manner when projected onto the wafer. Even under conditions of variable beam blur of the lithographic apparatus, line-width variation is reduced, yielding more accurate pattern transfer.
The foregoing and additional features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.